MONDAY, April 23 (HealthDay News) -- There may be a silver lining to the dark cloud of migraines: improved memory.

U.S. researchers have found that women with a history of migraines had less cognitive decline as they aged than women who didn't have the debilitating headaches.

"This was a complete surprise," noted study author Amanda Kalaydjian, a research fellow at the National Institute of Mental Health. "We found that people with migraines, specifically people with migraines with aura -- which is even more counterintuitive -- didn't even decline over time at all."

Kalaydjian's team published its finding in the April 24 issue of Neurology. Her research was conducted while a doctoral student at Johns Hopkins School of Public Health.

Other experts were similarly surprised by the finding.

"It's very surprising to me that this risk factor would appear to be protective," said Dr. Richard Lipton, director of the Montefiore Headache Center. "But this is the best longitudinal data we have on migraine, so I am left feeling cautiously optimistic."

Migraines are a particularly severe form of headache. They often occur on one side of the head and can involve visual disturbances ("aura"), sensitivity to light, nausea and vomiting. Migraines can last hours or days.

The headaches' causes remain elusive, although dietary and food factors, such as red wine, may play a role for some people. Researchers in Philadelphia are even looking into whether a common heart defect may play a role in migraine for some individuals.

Thus far, the evidence on migraines and cognitive functioning had been mixed. Some studies found no association and some found that people with migraines ("migraineurs") actually performed less well in tasks involving attention, verbal ability and memory.

"Some [previous studies] showed deficiencies in people with migraines and some didn't, but there were a lot of problems with past studies because they were very small or clinic-based," Kalaydjian said. "It's hard to generalize."

There have been virtually no studies that looked at people over time, she added.

This study involved 1,448 women, 204 of who suffered migraines. All women underwent a series of cognitive tests beginning in 1993 and again about 12 years later.

All of the affected women also had a long history of migraines. "Our thinking was . . . maybe, over time, migraines might result in these subtle insults to the brain," Kalaydjian explained. Scientists have hypothesized that migraine attacks might have a cumulative effect of damage to the brain.

The study didn't show that, however. Migraineurs did perform worse on cognitive tests (such as word recall) at the beginning of the study, but over the course of the entire study their performance actually declined 17 percent less overall than women without migraine.

Women over 50 who had migraines showed the least amount of cognitive decline, the researchers noted.

It's unclear why such a discrepancy would exist but Kalaydjian says certain medication and lifestyle characteristics of migraine sufferers might be worth exploring.

"People with migraines tend to stay away from alcohol, so we might have people that drink less and sleep more, because lack of sleep results in more headaches," she said. "They might take more vitamins and supplements because they're more health-conscious."

"One study isn't enough but it lays the groundwork for future studies," Kalaydjian said. "It brings up the point that maybe this is something that should be looked into, maybe there's a beneficial side effect of having this pain."